Rename discriminator to waf everywhere (closes #312)

The command is now `sww waf`, and the package is `internal/waf`. Types,
functions, files, tests, comments, docs, the Dockerfile, the runit
script, `script/`, compose examples, the log field `waf_line` and the
`X-From-Waf` test header follow. No behaviour changes, and no setting
changes name: rproxy already finds the waf through `SWRP_WAF_BACKEND`.

Done with one `sed -i` (Discriminator and DISCRIMINATOR to WAF,
discriminator to waf) over the files `git grep -i discriminator`
listed, as sneak allowed for this rename, then `git mv` for the
package and files. By hand afterwards: the header's spelling, which
the linter requires, and the padding after `waf` in `sww`'s usage
text.

Model: opus-5-5

internal/rproxy/request.go

@@ -16,16 +16,16 @@ import (
 	"sync/atomic"
 	"time"
 
-	"sneak.berlin/go/smallwebwaf/internal/discriminator"
 	"sneak.berlin/go/smallwebwaf/internal/requestlog"
 	"sneak.berlin/go/smallwebwaf/internal/rules"
+	"sneak.berlin/go/smallwebwaf/internal/waf"
 )
 
 // flushAfterEachWrite has ReverseProxy pass on each part of the app's answer as
 // soon as it arrives.
 const flushAfterEachWrite time.Duration = -1
 
-// reportStatusMax is the highest status discriminator takes in a report. An app can
+// reportStatusMax is the highest status waf takes in a report. An app can
 // send a higher one, up to 999, and the visitor gets that as it is.
 const reportStatusMax = 599
 
@@ -60,14 +60,14 @@ type request struct {
 	peerTrusted bool
 	start       time.Time
 
-	// disposition is what is done with the request: discriminator's valid disposition,
+	// disposition is what is done with the request: waf's valid disposition,
 	// or SWRP_DEFAULT_DISPOSITION. It is "" when neither gave one.
 	disposition string
-	// answered is true when discriminator gave disposition, which makes a report due,
+	// answered is true when waf gave disposition, which makes a report due,
 	// and byDefault when SWRP_DEFAULT_DISPOSITION did.
 	answered  bool
 	byDefault bool
-	// asn and country are discriminator's X-Client-ASN and X-Client-Country, for the
+	// asn and country are waf's X-Client-ASN and X-Client-Country, for the
 	// app.
 	asn, country string
 
@@ -131,14 +131,14 @@ func (rq *request) answerHealth() {
 // visitor too slow to send it is answered 408. For a malformed chunk, or a
 // visitor that went away or stopped its sending side, the connection is closed
 // without an answer. A body over SWRP_MAX_REQUEST_SIZE goes on with the part
-// read, so that discriminator is asked first; passToApp then refuses it.
+// read, so that waf is asked first; passToApp then refuses it.
 func (rq *request) readFirstPartOfBody() bool {
 	if rq.body == nil {
 		return true
 	}
 
 	_ = rq.rc.SetReadDeadline(rq.requestDeadline())
-	held, err := io.ReadAll(io.LimitReader(rq.body, discriminator.QuestionBodyMaxBytes))
+	held, err := io.ReadAll(io.LimitReader(rq.body, waf.QuestionBodyMaxBytes))
 	// From here on, the request timer ends a read of the rest of the body, so that
 	// the answer can name the side rproxy was waiting on.
 	_ = rq.rc.SetReadDeadline(time.Time{})
@@ -200,7 +200,7 @@ func (rq *request) forward(ctx context.Context) {
 // rewrite makes the request the app receives: the visitor's request, unchanged,
 // sent to SWRP_UPSTREAM_URL, with the forwarded headers and the request's id set,
 // without any X-Client-ASN or X-Client-Country the visitor sent, and with
-// discriminator's.
+// waf's.
 func (rq *request) rewrite(pr *httputil.ProxyRequest) {
 	upstream := rq.h.config.UpstreamURL
 	pr.Out.URL.Scheme = upstream.Scheme
@@ -333,7 +333,7 @@ func (rq *request) answer(status int) {
 // handler has returned, after finish has written the log line and sent the report.
 // Without Content-Length, the flush would send the body in chunks, the last of
 // which would still wait for the handler. A HEAD's answer has no body, so any
-// Content-Length it has stays as discriminator gave it.
+// Content-Length it has stays as waf gave it.
 func (rq *request) send(status int, body []byte) {
 	if rq.in.Method != http.MethodHead {
 		rq.out.Header().Set("Content-Length", strconv.Itoa(len(body)))
@@ -379,7 +379,7 @@ func (rq *request) refuse(status int) {
 	}
 }
 
-// finish ends the request's time limits, writes its log line and, if discriminator
+// finish ends the request's time limits, writes its log line and, if waf
 // answered the question, sends the report. ctx is the request's own context.
 func (rq *request) finish(ctx context.Context) {
 	rq.stopTimers()
@@ -416,7 +416,7 @@ func (rq *request) finish(ctx context.Context) {
 		return
 	}
 
-	report := &discriminator.Report{
+	report := &waf.Report{
 		RequestID:       rq.id,
 		Status:          min(rq.out.status, reportStatusMax),
 		RequestBytes:    requestBytes,